1. Field of the Invention
The present invention relates to a process for removing sulfur oxides (hereinafter referred to as "SO.sub.x ") from a combustion exhaust gas with high absorption efficiency in accordance with a wet lime/gypsum method and an apparatus for carrying out this process.
2. Description of the Related Art
Processes have been known in which a combustion exhaust gas is treated in accordance with a wet lime/gypsum method to remove SO.sub.x from the gas. Some examples of conventional technology can be found in U.S. Pat. No. (USP) 4,374,812, wherein the addition of oxygen containing gas for oxidizing sulfur oxides is mainly discussed, U.S. Pat. No. 4,614,645, which discloses a method for treating effluent in an exhaust gas treatment apparatus, and U.S. Pat. No. 4,696,804, which discloses a method for treating SO.sub.2, SO.sub.3 and dust using a single tower, as well as in British Patent Application GB 2169888A, wherein a single column for wet desulfurization is discussed. However, when a conventional wet lime/gypsum method is used, the combustion exhaust gas is desulfurized merely to such an extent that the concentration of SO.sub.x in the desulfurized gas is several tens of ppm, because the conventional method is restricted by the required purity of calcium compounds, such as the by-product gypsum, produced from an absorbent ingredient material and by the economical amount of lime used.